Origin of the Selectivity of alpha-Dicarbonyl Reagents for Arginyl Residues of Anion-Binding Sites

Fluc family fluoride channels protect microbes against ambient environmental fluoride by undermining the cytoplasmic accumulation of this toxic halide. These proteins are structurally idiosyncratic, and thus the permeation pathway and mechanism have no analogy in other known ion channels. Although fluoride binding sites were identified in previous structural studies, it was not evident how these ions access aqueous solution, and the molecular determinants of anion recognition and selectivity have not been elucidated. Using x-ray crystallography, planar bilayer electrophysiology and liposome-based assays, we identify additional binding sites along the permeation pathway. We use this information to develop an oriented system for planar lipid bilayer electrophysiology and observe anion block at one of these sites, revealing insights into the mechanism of anion recognition. We propose a permeation mechanism involving alternating occupancy of anion binding sites that are fully assembled only as the substrate approaches.

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The red cell band 3 protein: its role in anion transport

Philosophical Transactions of the Royal Society of London Series B Biological Sciences ◽

10.1098/rstb.1982.0147 ◽

1982 ◽

Vol 299 (1097) ◽

pp. 497-507 ◽

Cited By ~ 16

Keyword(s):

Binding Sites ◽

Band 3 ◽

Anion Transport ◽

Anion Binding ◽

Hydrophobic Residues ◽

Ping Pong ◽

Hydrophilic Residues ◽

Aqueous Core ◽

Positively Charged

Studies of anion transport across the red blood cell membrane fall generally into two categories: (1) those concerned with the operational characterization of the transport system, largely by kinetic analysis and inhibitor studies; and (2) those concerned with the structure of band 3, a transmembrane peptide identified as the transport protein. The kinetics are consistent with a ping-pong model in which positively charged anion-binding sites can alternate between exposure to the inside and outside compartments but can only shift one position to the other when occupied by an anion. The structural studies on band 3 indicate that only 60 % of the peptide is essential for transport. That particular portion is in the form of a dimer consisting of an assembly of membrane-crossing strands (each monomer appears to cross at least five times). The assembly presents its hydrophobic residues toward the interior of the bilayer, but its hydrophilic residues provide an aqueous core. The transport involves a small conformational change in which an anion-binding site (involving positively charged residues) can alternate between positions that are topologically in and topologically out.

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Functional arginyl residues as NADH binding sites of alcohol dehydrogenases

Biochemistry ◽

10.1021/bi00718a019 ◽

1974 ◽

Vol 13 (21) ◽

pp. 4361-4370 ◽

Cited By ~ 157

Author(s):

Louis G. Lange ◽

James F. Riordan ◽

Bert L. Vallee

Keyword(s):

Binding Sites ◽

Alcohol Dehydrogenases ◽

Arginyl Residues

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Interactions between transport inhibitors at the anion binding sites of the band 3 dimer

Biochemistry ◽

10.1021/bi00521a001 ◽

1981 ◽

Vol 20 (18) ◽

pp. 5095-5105 ◽

Cited By ~ 51

Author(s):

Ian G. Macara ◽

Lewis C. Cantley

Keyword(s):

Binding Sites ◽

Band 3 ◽

Anion Binding ◽

Transport Inhibitors

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Use of ionic and zwitterionic (Tris/BisTris and HEPES) buffers in studies on hemoglobin function

Journal of Applied Physiology ◽

10.1152/jappl.1992.72.4.1611 ◽

1992 ◽

Vol 72 (4) ◽

pp. 1611-1615 ◽

Cited By ~ 70

Author(s):

R. E. Weber

Keyword(s):

Binding Sites ◽

Ionic Composition ◽

Oxygen Affinity ◽

Chloride Concentration ◽

Anion Binding ◽

Chloride Binding ◽

Ph Values ◽

Two Temperatures ◽

Ethanesulfonic Acid ◽

Chloride Concentrations

The functional characteristics of hemoglobin (Hb) depend on oxygenation-linked proton and anion binding and thus on solvent buffer groups and ionic composition. This study compares the oxygenation properties of human Hb in ionic [tris(hydroxymethyl)aminomethane (Tris) and BisTris] buffers with those in zwitterionic N-2-hydroxy-ethylpiperazine-N′-2-ethanesulfonic acid (HEPES) buffer under strictly controlled chloride concentrations at different pH values, two temperatures, and in the absence and presence of the erythrocytic cofactor, 2,3-diphosphoglycerate (DPG). In contrast to earlier studies (carried out at the same or different chloride concentrations) it shows only small buffer effects that are manifested at low chloride concentration and high pH. These observations suggest chloride binding to the Tris buffers, which reduces the interaction with specific chloride binding sites in the Hb. The findings indicate that HEPES allows for more accurate assessment of Hb-oxygen affinity and its anion and temperature sensitivities than ionic buffers and advocates standard use of HEPES in studies on Hb function. Precise oxygen affinities of Hb dissolved in both buffers are defined under standard conditions.

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Highly Efficient, Tripodal Ion-Pair Receptors for Switching Selectivity between Acetates and Sulfates Using Solid–Liquid and Liquid–Liquid Extractions

International Journal of Molecular Sciences ◽

10.3390/ijms21249465 ◽

2020 ◽

Vol 21 (24) ◽

pp. 9465

Author(s):

Marta Zaleskaya ◽

Łukasz Dobrzycki ◽

Jan Romański

Keyword(s):

Binding Sites ◽

Liquid Extraction ◽

Ion Pair ◽

Anion Binding ◽

Binding Modes ◽

Anion Receptor ◽

X Ray ◽

Liquid Liquid Extraction ◽

Solid Liquid Extraction ◽

Solid Liquid

A tripodal, squaramide-based ion-pair receptor 1 was synthesized in a modular fashion, and 1H NMR and UV-vis studies revealed its ability to interact more efficiently with anions with the assistance of cations. The reference tripodal anion receptor 2, lacking a crown ether unit, was found to lose the enhancement in anion binding induced by presence of cations. Besides the ability to bind anions in enhanced manner by the “single armed” ion-pair receptor 3, the lack of multiple and prearranged binding sites resulted in its much lower affinity towards anions than in the case of tripodal receptors. Unlike with receptors 2 or 3, the high affinity of 1 towards salts opens up the possibility of extracting extremely hydrophilic sulfate anions from aqueous to organic phase. The disparity in receptor 1 binding modes towards monovalent anions and divalent sulfates assures its selectivity towards sulfates over other lipophilic salts upon liquid–liquid extraction (LLE) and enables the Hofmeister bias to be overcome. By changing the extraction conditions from LLE to SLE (solid–liquid extraction), a switch of selectivity from sulfates to acetates was achieved. X-ray measurements support the ability of anion binding by cooperation of the arms of receptor 1 together with simultaneous binding of cations.

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